The present invention relates to a deposition method of thin films required for manufacturing semiconductor devices, flat panel devices, and etc.
Such thin films may include metal films, insulator films such as metal oxide films, metal nitride films and etc., films for capacitors, interconnects and electrodes, inorganic films used for diffusion prevention, and etc.
These thin films may be formed by a physical vapor deposition, for example a sputtering process. The sputtering process, however, forms thin films with poor step coverage, so a chemical vapor deposition method is usually employed to improve the step coverage.
One of the most common chemical vapor depositions of the prior art is carried out by an apparatus as shown in FIG. 1A. Referring to FIG. 1A, process gases or other reactants 11, 12, 13 are supplied into a reactor 1, respectively, through mass flow controllers 21, 22, 23 and valves 30, 31, 32. In this case, a shower head 4 is utilized to obtain uniform flow 5 of the process gases. When a source material is liquid or solid having low equilibrium vapor pressures, a vaporizer 16 is also employed that can heat the source material in a suitable temperature to vaporize and can supply the vaporized source material into the reactor 1 with the carrier gas 13. When the vaporizer is employed, the initial portion of the source material carried by the carrier gas 13 is exhausted via a bypass valve 33 and an outlet tube 18 due to the fluctuation of flow rate and source material concentration. Then, the bypass valve 33 is shut off and a valve 32 connected to a central supplying tube 17 is opened to supply the carrier gas into the reactor 1.
The chemical vapor deposition of the prior art performed in this apparatus has the following features: At first, all process gases 11, 12, 13 required for the deposition are supplied into the reactor 1 at the same time so that the film is continuously deposited during the process times 11xe2x80x2, 12xe2x80x2, 13xe2x80x2 as in an example shown in FIG. 1B. At second, the shower head 4 is usually employed to make uniform flow 5 of the process gases on the surface of a substrate.
This method has the following disadvantages: At first, since all process gases exist within the reactor at the same time, the process gases may react in gas phase thereby can deteriorate step coverage of the deposited film and/or produce particles which contaminate the reactor. At second, when using a metal-organic compound as a source material, it is difficult to deposit the film that does not contain carbon impurities. At third, in the case of depositing a multi-component film, all the reactant materials must react simultaneously while the supply of each reactant material is controlled separately by mass flow of the carrier gas, so it is very difficult to control the composition of the deposited film precisely.
To overcome the foregoing problems, a method is proposed in which the process gases are supplied separately as time-divisional pulses rather than supplied continuously.
An example of supplying process gases in this deposition method is shown in FIG. 2A. Valves in a gas introducing part can be opened or closed so that the process gases can be supplied cyclically as time-divisional pulses into the reactor without being mixed with each other.
Referring to FIG. 2A, it can be seen that the process gases 11, 12, 13 in FIG. 1A are supplied in a cycle Tcycle of 13xe2x80x2, 12xe2x80x2, 11xe2x80x2 and 12xe2x80x2. A film can be deposited by repeating this cycle. In general, purge gas 12 is supplied between the supply pulses of the reactants 11 and 13 so that the remaining reactants are removed from the reactor before the next reactant is supplied.
Hereinafter, a time-divisional deposition mechanism will be described. Chemical adsorption temperatures of the reactants onto the substrate are generally lower than thermal decomposition temperatures of the reactants. Therefore, when a deposition temperature is maintained higher than the chemical adsorption temperature of the reactant onto the substrate and lower than the thermal decomposition temperature of the reactant, the reactant supplied into the reactor only adsorbs chemically onto the surface of the substrate rather than decomposes. Then, the remaining reactant is exhausted out of the reactor by the purge gas supplied into the reactor. After that, another reactant is introduced into the reactor to react with the reactant adsorbed on the surface, and thus form a film. Because the reactant adsorbed on the substrate cannot form more than one molecular layer, film thickness formed in one supply cycle Tcycle is constant regardless of amount or time of the supplied reactants. Therefore, as shown in FIG. 2B, the deposited film thickness is saturated as the supplying time elapses. In this case, the deposited film thickness is controlled only by the number of the repeated supply cycles.
In the other hand, when the deposition process temperature is no lower than the thermal decomposition temperature of the reactants, the deposited film thickness is proportional to the supply time of the reactants in the supply cycle because the reactants introduced into the reactor decompose continuously to form films on the substrate. In this case, deposited film thickness according to the supply time of the reactants is shown in FIG. 2C.
However, the foregoing time-divisional deposition has problems as follows:
At first, the reactants used in the deposition process must react readily. Otherwise it is difficult to form a film by time-divisional deposition. In this case, a method is required that facilitate the chemical reaction even at low temperatures.
At second, the exhausting part of the apparatus may be contaminated with particles due to the reactions between the reactants. The gas-introducing part and the reactor may not be contaminated with the particles due to the reactions of the reactants because the reactants are separated by the purge gas. In the other hand, the exhausting part may be easily contaminated with particles because the reactants mix and react with each other at exhaust.
At third, it is required to supply inert purge gas between the reactant supply pulses to prevent gas-phase reactions in the gas-introducing part and the reactor, so the gas-supply cycle is complex, the time for a supply cycle is longer than absolutely necessary, and thus the deposition is slow.
A method is disclosed in the U.S. Pat. No. 5,916,365 in which a film is formed by repeating a gas-supply cycle, i.e., supplying first reactant gas into a reactor, exhausting remaining reactant gas within the reactor by a vacuum pump, supplying second reactant gas which is activated by passing through a radical generator using an RF power or other means, and exhausting remaining reactant gas by the vacuum pump.
The exhaust rate of the vacuum pump decreases as the pressure decreases, so it takes long time to exhaust the remaining reactant gases from the reactor with the vacuum pump. Therefore, in this method, it is difficult to have high growth rate of the film per unit time when it desired to exhaust the remaining reactant gases completely. When the exhausting time is too short, the reactant gases remain in the reactor so that the two reactant gases mix and react in gas phase. Furthermore, in the method of the U.S. Pat. No. 5,916,365, it is difficult to maintain stable plasma in the reactor because the supply and exhaust of the reactant gases cause wide pressure variation in the reactor.
Therefore, it is an object of the present invention to provide a method which can form a thin film effectively even if reactants do not react readily in a time-divisional source supply chemical vapor deposition method.
It is another object of the present invention to provide a method which can minimize supply time of a purge gas in a gas-supplying cycle to reduce cycle time in a time-divisional source supply chemical vapor deposition.
It is further object of the present invention to provide a method which can reduce particle contamination of the apparatus at the exhausting part of an apparatus for time-divisional source supply chemical vapor deposition.
In order to realize those foregoing objects, the present invention provides a method used for a chemical vapor deposition in which source gases for forming a thin film are supplied into a reactor in a time-divisional manner so that they may not be mixed with each other in the reactor. In the method of the invention, the process gases are activated into plasma to faciliate the film formation, wherein plasma is generated synchronously with gas supply cycle.
For more clear description, process gases are classified as three kinds:
At first, the process gas that thermally decomposes to form a solid film is called a deposition gas. The deposition gas includes, for example, titanium-organic compound used for chemical vapor deposition for forming a TiN film.
At second, the process gas that does not decompose by itself or does not form a solid film upon self-decomposition, however, forms a solid film when reacts with a deposition gas is called a reactant gas. The reactant gas includes, for example, ammonia used in a chemical vapor deposition process for forming a nitride film, and oxygen gas used in a chemical vapor deposition process for forming a oxide film.
At third, the other inert process gas that is supplied between the supplies of the deposition gas and the reactant gas to separate the deposition gas and the reactant gas is called a purge gas. In general, helium, argon, nitrogen gas and etc. are used for a purge gas. Those gases contain the constituent element of the film may also used for a purge gases if they do not react with a deposition gas. In this case, the purge gas can be used for a reactant gas when activated by plasma.
Therefore, one of the most evident features of the present invention, in a chemical vapor deposition which forms a film on a substrate by supplying process gases which include a deposition gas, a reactant gas, and a purge gas into a reactor by repeating cycles of time-divisional gas supply, is to provide a method of generating plasma on the substrate synchronously with the supply cycles to activate at least one of the process gases. In this case, the plasma is generated synchronously with the supply cycle of the reactant gas.
Also, when a purge gas contains constituent elements of a film material and a reactant gas contains the other constituent elements of the film material and the purge gas does not substantially react with the reactant gas, plasma may be preferably generated synchronously during the supply cycle of the purge gas.
In the other hand, a film is deposited by alernate supply of only a deposition gas and a purge gas without any reatanct gas into a reactor. In this case, the purge gas preferably contains constituent elements of a film material and does not react substantially react with the deposition gas if not activated; wherein plasma is preferably generated synchronously at least in part during the supply cycle of the purge gas to facilitate the reaction of the purge gas with the deposition gas.
The films deposited by above methods may be heat-treated after the deposition.